1. Field of the Invention
The present invention relates to an apparatus for batch production of a liquid crystalline polymer and to a method for continuous production of a liquid crystalline polymer using the apparatus. More particularly, the present invention relates to an apparatus for batch production of a liquid crystalline polymer, such as an aromatic polyester resin or an aromatic polyester amide resin, which tends to be oxidized or deteriorated when heated in the air, as well as to a method for continuous production of a liquid crystalline polymer using the apparatus.
2. Description of the Related Art
Conventionally, an optically anisotropic liquid crystalline polymer, such as an aromatic polyester resin or an aromatic polyester amide resin, is produced in the following manner by use of an apparatus for batch production as shown in FIG. 5. A liquid crystalline polymer is formed through reaction effected within a reactor 1 shown in FIG. 5. The thus-formed viscous polymer is discharged under pressure through a die-plate 3 having a number of holes 4 formed therein and attached to the bottom end of a die-head 2, which, in turn, is attached to a lower portion of the reactor 1. Passing through the holes formed in the die-plate 3, the viscous polymer is discharged in the form of strands 5, which are then cut into pellets having a predetermined size.
The die-head 2 includes a discharge valve 6 attached to the bottom portion of the reactor 1 and adapted to open/close a discharge port 1a, through which a viscous polymer is discharged; a jacket 8 having a polymer chamber 7 formed therein so that the viscous polymer is uniformly distributed over the die-plate 3 attached to the bottom end thereof, and allowing a heat-insulating fluid to flow along the outer wall thereof; and the die-plate 3 attached to the bottom end of the jacket 8. In this manner, the die-head 2 forms a discharge path 9 for the viscous polymer.
However, the following problem is involved in continuous production of a liquid crystalline polymer in batches using the above-mentioned apparatus for batch production of a liquid crystalline polymer (as used herein, the term xe2x80x9ccontinuousxe2x80x9d in xe2x80x9ccontinuous productionxe2x80x9d means that an intermediate step, such as washing and drying, is not involved between production of one batch and production of the next batch). Since the die-plate 3 is attached directly to the jacket 8 of the die-head 2, after discharge of one batch of liquid crystalline polymer, a portion of the produced liquid crystalline polymer remains at, for example, a narrow portion 9a of the discharge path 9; i.e., a portion defined by the end of the discharge valve 6 and the inner wall of the polymer chamber 7 of the die-head 2. As a result, yield of pellets decreases.
Also, upon coming into contact with the air which enters the polymer chamber 7 through the holes 4 formed in the die-plate 3, the residual liquid crystalline polymer is oxidized or deteriorated; for example, discolors or carbonizes. When the next batch of liquid crystalline polymer is discharged, the deteriorated liquid crystalline polymer may clog the holes 4 formed in the die-plate 3, may disturb uniform formation of strands, may mingle in strands in the form of black specks causing impairment in quality, or may force interruption of cutting of strands when a lump thereof is caught by a cutter.
Accordingly, the conventional continuous production process of a liquid crystalline polymer using a batch type apparatus requires a lot of time and labor for removal of the above-mentioned residual liquid crystalline polymer; i.e., cleaning of the polymer chamber 7, or removal of oxidized, deteriorated, discolored and carbonized liquid crystalline polymer, resulting in a great decrease in production efficiency.
Japanese Patent Application Laid-Open (kokai) No. 192403/1994 discloses a method for continuous batch polymerization of a liquid crystalline polyester. According to the disclosed method, a polymer melt is discharged from a polymerizer such that the amount of residual polymer melt is not greater than 30 kg per cubic meter of internal volume of the polymerizer, followed by charge of material for production of the next batch. Since the residual polymer decreases the effective internal volume of the polymerizer available for polymerization, the utilization efficiency of the polymerizer is reduced accordingly. Also, it may happen that the melting point of the residual polymer increases, and the resultant residual polymer may migrate into the next batch of polymer, causing impairment in quality. Also, the migration of the residual polymer into the next batch of polymer disturbs smooth discharge of polymer.
An object of the present invention is to provide an apparatus for batch production of a liquid crystalline polymer capable of preventing oxidation or deterioration of residual liquid crystalline polymer in a certain batch to thereby prevent potential clogging of a die with deteriorated residual liquid crystalline polymer in the course of discharge of the next batch of liquid crystalline polymer, with a resultant improvement in productivity or yield, and to thereby improve the quality of liquid crystalline polymer discharged therefrom, as well as to provide a method for continuous production of a liquid crystalline polymer using the apparatus.
Accordingly, the present inventors have intensively studied the mechanisms of oxidation and deterioration of residual liquid crystalline polymer present in a polymer chamber of a die-head, characteristics of various kinds of liquid crystalline polymers, the structure and oxygen shutoff mechanisms of the die-head, the installation position, shape and structure of a slit valve, and the relative timing of operation of the slit valve and a discharge valve, among other factors, thereby achieving the present invention.
The present invention provides a batch type apparatus for producing a liquid crystalline polymer, comprising: a reactor for producing a liquid crystalline polymer capable of forming an anisotropic melt phase, the reactor having a discharge port at a lower portion thereof; a first gas-pressurizing means attached to the reactor for discharging under pressure the liquid crystalline polymer by use of an inert gas; a die-head including, at one end portion thereof, a discharge valve which opens and closes the discharge port, at a middle portion thereof, an internal chamber which communicates with the discharge port and is heated and regulated from the peripheral surface thereof, and at the other end portion thereof, an opening which forms an end portion of the internal chamber; a shut-off valve connected to the other end portion of the die-head and capable of opening and closing the opening; and a die-plate disposed at the opening of the shut-off valve.
Preferably, in the batch type apparatus according to the present invention, the shut-off valve is a slit valve which has a plurality of holes capable of establishing communication between the opening side and the die-plate side and which shuts off the opening side from the atmospheric air when closed.
Preferably, in the batch type apparatus according to the present invention, the die-head has a pressurized gas inlet at an upper portion of the internal chamber and the pressurized gas inlet is connected to a second gas-pressurizing means which supplies an inert gas.
The present invention further provides a method for continuously producing a liquid crystalline polymer using the batch type apparatus according to the present invention, the method comprising the steps of: opening the shut-off valve and the discharge valve after completion of formation of the liquid crystalline polymer in the reactor, and discharging the polymer outward via the die-head and the die-plate, while pressurizing the polymer in the reactor by use of the inert gas fed from the first gas-pressurizing means; conducting an operation for stopping discharge of the liquid crystalline polymer, after completion of discharge of the liquid crystalline polymer, so as to close the shut-off valve and the discharge valve while discharging the inert gas; when a predetermined period of time has elapsed and a liquid crystalline polymer formed in the next batch is to be discharged, opening again the shut-off valve and the discharge valve, while pressurizing the polymer in the reactor by use of the inert gas fed from the first gas-pressurizing means, to thereby conduct an operation for starting discharge of the polymer outward through the die-head and the die-plate; and repeating, for a prescribed number of times, the above-mentioned series of operations for discharging of the polymer, stopping discharge of the polymer, and starting discharge of the polymer.
The sequence of opening the shut-off valve and the discharge valve is not particularly limited. For example, (1) the shut-off valve is first opened, and then the discharge valve is opened, (2) the discharge valve is first opened, and then the shut-off valve is opened, or (3) the shut-off valve and the discharge valve are opened substantially concurrently. When the withstand pressure of the shut-off valve is low, method (1) or (3) is preferred. Similarly, the sequence of closing the shut-off valve and the discharge valve is not particularly limited. For example, (4) the shut-off valve is first closed, and then the a discharge valve is closed, (5) the discharge valve is first closed, and then the shut-off valve is closed, or (6) the shut-off valve and the discharge valve are closed substantially concurrently. When the withstand pressure of the shut-off valve is low, method (5) or (6) is preferred. The same is applied to the remainder of the description appearing in this section.
The present invention further provides another method for continuously producing a liquid crystalline polymer using the batch type apparatus according to the present invention, the method comprising the steps of: opening the shut-off valve and the discharge valve after completion of formation of the liquid crystalline polymer in the reactor, and discharging the polymer outward via the die-head and the die-plate, while pressurizing the polymer in the reactor by use of the inert gas fed from the first gas-pressurizing means; conducting an operation for stopping discharge of the liquid crystalline polymer, after completion of discharge of the liquid crystalline polymer from the reactor, so as to close the shut-off valve and the discharge valve while discharging the inert gas; starting formation of a liquid crystalline polymer of the next batch in the reactor after the discharge valve is closed, and, after elapse of a required period of time, introducing under pressure the inert gas from the second gas-pressurizing means into the internal chamber of the die-head via a gas inlet formed at an upper portion of the internal chamber of the die-head, opening the shut-off valve so as to discharge the polymer in the die-head and the shut-off valve, and then closing again the shut-off valve while discharging the inert gas outward, thereby conducting an operation of stopping discharge of the polymer in the die-head; when a predetermined period of time has elapsed and a liquid crystalline polymer formed in the next batch is to be discharged, opening again the shut-off valve and the discharge valve, while pressurizing the polymer in the reactor by use of the inert gas fed from the first gas-pressurizing means, to thereby conduct an operation for starting discharge of the polymer outward through the die-head and the die-plate; and repeating, for a prescribed number of times, the above-mentioned series of operations for discharging of the polymer, stopping discharge of the polymer, stopping discharge of the polymer in the die-head, and starting discharge of the polymer of the next batch.
In the methods according to the present invention, the liquid crystalline polymer may be an aromatic polyester resin or an aromatic polyester amide resin.
In the methods according to the present invention, the liquid crystalline polymer may be an aromatic polyester amide resin being composed of p-hydroxy benzoic acid, 6-hydroxy-2-naphthoic acid, 4,4xe2x80x2-dihydroxy biphenyl, terephthalic acid, and p-aminophenol, as constitutional monomer components.
In the methods according to the present invention, the liquid crystalline polymer is an aromatic polyester resin being composed of p-hydroxy benzoic acid, and 6-hydroxy-2-naphthoic acid, as constitutional monomer components.
Through employment of the shut-off valve and through combination of shut-off valve operation, discharge valve operation, and discharge of an inert gas, the amount of residual liquid crystalline polymer is decreased greatly, and oxidation or deterioration, such as discoloration or carbonization, of the residual liquid crystalline polymer can be prevented.
Thus, discharge of a certain batch of liquid crystalline polymer does not encounter clogging of the die plate with residual liquid crystalline polymer of the preceding batch. Also, quality and yield of a produced liquid crystalline polymer can be improved. Further, since continuous production can be carried out without performance of cleaning in the middle, the cycle time of production can be shortened, and production efficiency can be improved.
Through employment of the pressurized gas inlet formed at an upper portion of the internal chamber of the die-head, and the gas-pressurizing means for supply of a pressurized inert gas to the pressurized gas inlet, production of the second batch can be immediately started upon completion of discharge of the first batch of the liquid crystalline polymer from the reactor, thereby further improving production efficiency.
Through introduction of a pressurized inert gas into the upper portion of the internal chamber of the die-head through the pressurized gas inlet, residual liquid crystalline polymer present in the die-head and die-plate can be free of oxidation or deterioration, such as discoloration or carbonization, thereby improving quality and yield of a liquid crystalline polymer.